It is desirable to decrease the sulfur content of molten iron, such as pig iron and cast iron, for use in steel production. Initial sulfur levels of molten iron generally range from about 0.015 to about 0.15 wt. %S. Low sulfur content iron, generally below about 0.005 wt. %S, is a prerequisite for low sulfur steels, which have improved physical properties, lower inclusion contents and decreased cracking tendency.
Desulfurization usually is effected during transfer from the blast furnace producing the molten iron to the steel-making operation. For this purpose, desulfurization agents, including lime, calcium carbide and magnesium-containing reagents, have been employed. Typical prior art known to the applicants includes U.S. Pat. Nos. 3,998,625, 4,266,969 and 4,277,279 and Canadian Patents Nos. 1,188,520 and 1,188,521. Many other prior patents are also referred to in this prior art.
These prior art processes involve injection into the molten iron of a single powder mixture, which may involve two or more reagents, including mixtures of lime and magnesium and calcium carbide and magnesium. When such mixtures are used, the components are injected into the molten iron simultaneously from the start to finish of the desulfurizing process. Usually, such mixtures contain the same quantity of each reagent during the injection process. In U.S. Pat. No. 3,998,625, the desulfurizing process.